Lecture : Chapters 19-20 Community Dynamics and Landscape Dynamics Flashcards
Community
Groups of interacting species taht occur together at the same place and time
Characteristics of communities
species richness, evenness, diversity, composition
How do communities change?
Agents of change act on communities across all temporal and spatial scales
zonation
change in community structure across the landscape
succession
change in community structure over time
gradual change
subtle changes include gradual turnover of dominant speices (due to competition), predation and disease
catastrophic change
coral death due to bleaching events, the tsuanmi of 2004 which resulted in replacement of some coral species with other species, or no replacement at all
Succession
gradual change in species composition in communities over time
disturbance
restarts succession
succession
results from both biotic and abiotic factors
abiotic factors
form of climate, soils, nutrients and water, vary over daily, seasonal, decadal and longer time scales
disturbance
discrete event that disrupts community structure and function by injuring or killing some individuals. It also creates opportunities for other individuals.
Diseases
initiate community change by causing death or slow growth of a species
ecosystem engineers
keystone species can influence community change
sere
entire sequence of succession including all comunities during the process
seral stage
a distinct community at a point in the succession. Each stage has a characteristic structure and species composition
early successional species
high fecundity, effective dispersal, rapid growth, smaller size, good colonizers
late successional species
low fecundity, less effective dispersal and colonization, slower growth rate, larger and live longer. However, they have the ability to grow, surive and compete when resources are scarce
primary succession
involves the colonization of habitats devoid of life (e.g. volcanci rock, galicaiton). Very slow. Inhospitable initial conditions
Seconday succession
involves reestablishment of a community in which some, but not all, organissm have been destryoed by disturbance (e.g. logging, fire, agriculture). Occurs on previously occupied sites
Hetereotrophic succession
refers to succession in heterotrophic commmunities involved in decomposition.
studies of succession often vocus on vegetative change, but the roles of animals, fungi, bacteria and other microbes are equally important
Henry Cowles
A pioneer of “dynamic ecology”, especially on the sand dunes of Lake Michigan. he developed the concept of ecological succession
intermediate disturbance hypothesis, first proposed by Connell 1978
Species diversity should be greatest at intermediate levels of disturbance
At low levels of disturbance, competition determines diversity. At high disturbance levels, many species can not survive or establish
Three Models of Succession
Facilitation
Inhibition
Tolerance
Facilitation model
Early succesional species modify the environment in ways that benefit later successional species to invade and grow to maturity. The sequence of species facilitaions leads to a climax commnity
Climax community
Composed of dominant species that persist over many years and provide stability that can be maintained indefinitely. Only disturbance resets the system.
Inhibition model
involves strong competitive interactions. It assumes early species modify conditions in negative ways that hinder both early and later successional species from invading. Eventually early individuals and short-lived species die releasing space for long-lived species
Tolerance model
assumes the earliest species modify the environment, but in neutral ways that neither benefit nor inhibit later species. Later species can invade and grow as they can efficiently exploit the available resources
Landscape Dynamics
Landscape ecology emphasizes broad spatial scales and the ecological effects of the spatial patterning of ecosystems
Fragmentation
Usually accompanied by habitat loss
Results in
- decrease in total habitat area (and thus in total metapopulation size)
- increase in the number of populations
- decrease in average population size
- increase in the length of edges
- decrease in the proportion of “interior habitat”
Abiotic changes influence species composition and distribution
Abiotic changes in temperature, light and moisture at the edge of forests
Species composition changes as a function of edge
regional differences in species diversity are influenced by area and distance, which determine the balance between immigration and extinction rates
an important concept in biogeography is the species-area relationship: species richness increases with area sampled
Species-area curves plot species richness (S) of a sample against area (A) of the sample
The relationship between S and A is estimated by linear regression
S=zA+c
island
any kind of isolated area surrounded by dissimilar habitat
theory of island biogeography (MacArthur and Wilson, 1967)
A theoretical model to explain how area and distance to mainland influence the equilibrium numbe rof species on an island
Number of species depends on balance between immigration and extinction rates
Corridors
Strips of habitat with the designated or incidental function of increasing dispersal among populations
- act as travel pathways
- provide basic requirements for foraging, breeding, refugia
